Airtight walls & fixing stuff to them

[joe90]

1 minute ago, Nickfromwales said:

Did you have an AT test?

Yes and it was good, can’t remember the actually figure but the tester had never seen one that good (but he normally did estate houses ?) certainly below 3, my only leaks were around windows where timber had shrunk slightly (now rectified) and around the woodburner air duct.

5 minutes ago, Nickfromwales said:

Parge needs to be done before joists / wall plates go in / on, and before floor ( deck ) boards go down, to get to all the areas that are often overlooked.

Definitely ?

[Hastings]

Very puzzled by this discussion. I can't imagine a lasting airtightness achieved with anything other than flexible membranes and tapes. Hard materials like plaster and cement based parge coats will all develop cracks. Isn't making something airtight similar to making it watertight?

[Chanmenie]

37 minutes ago, Hastings said:

Very puzzled by this discussion. I can't imagine a lasting airtightness achieved with anything other than flexible membranes and tapes. Hard materials like plaster and cement based parge coats will all develop cracks. Isn't making something airtight similar to making it watertight?

 

You can probably apply the same thinking to tapes, do they lose adhesion over time ?  or peel due to movement or shrinkage,  once all covered up you'll never know

[Hastings]

Yes, that's right but the tapes and membranes are are designed and made to last at least the expected life of the building, claiming testing to 50-100 years.

 

I was very sceptical to begin with but after working with the materials myself, particularly the tape, I believe it. It is not like any tape I have ever experienced before. If you make a mistake it does not come off without breaking itself or the material it has stuck to, even to dirty gloves.

 

Rodents are a worry though. My build has 600mm thick stone cladding to keep them at bay but if I only had timber cladding I might have chosen a very different airtight solution.

 

 

[Nickfromwales]

11 hours ago, Hastings said:

Very puzzled by this discussion. I can't imagine a lasting airtightness achieved with anything other than flexible membranes and tapes. Hard materials like plaster and cement based parge coats will all develop cracks. Isn't making something airtight similar to making it watertight?

You use tapes and membranes strategically, alongside the parge coats etc. How good a job you do on the parge will reduce the amount of membrane / tape you consume, so use that to do the major gap filling alongside a quality closed cell air control foam ( Link  ) for a complete solution which will last a very long time.

 

We've had great results with Passive Purple, a spray on or brush applied ( 2 different types ) liquid airtight membrane, which we've recently applied over both parged and non-parged woodcrete ICF structures. Very happy to recommend Adam White ( supplier of the PP product  link ) whom I have spoken with at length for solutions to attain airtightness in my 2 most recent ( clients ) projects. He was very helpful indeed, and gave us great support for the correct selection, application and integration of the product, vs differing substrate types. He was also very well versed with the world of "passive house". With a recent very challenging Velox build he came out to site to go through everything wit me in person, without any promise of business(!!), and the agreed solutions and subsequent AT test results spoke for themselves .

 

We used the PP in key areas only, after a cementitious parge was first applied to all internal ( outer wall ) surfaces. It was primarily used in the window and door reveals to allow the AT tapes around the frames to have something airtight and uniform to adhere to, but was great for getting into acute angles / difficult junctions aka 'nooks an crannies'.

 

10 hours ago, Chanmenie said:

 

You can probably apply the same thinking to tapes, do they lose adhesion over time ?  or peel due to movement or shrinkage,  once all covered up you'll never know

Proper tapes and membranes stick to each other like shit to a blanket, and I pity anyone who applies them to areas where they then have to be removed from. The most important thing is to have the surfaces freshly cleaned / primed / dust and contamination-free to allow the tapes to work well and last a very very long time.

 

Mastics, membranes ( liquid or sheet ) and tapes, in conjunction with parge coating can ( and does ) work very well indeed. The devil as always is in the detail.

[Chanmenie]

@Nickfromwales great informative post thanks Nick.

So with your experience which parge would you say is best, simple sand cement or something like Soundcoat plus.

I was planning on doing exactly what you have suggested, parge all insides of external walls then detail tricky areas with PP or the Soudal equivalent.

[Nickfromwales]

1 minute ago, Chanmenie said:

@Nickfromwales great informative post thanks Nick.

So with your experience which parge would you say is best, simple sand cement or something like Soundcoat plus.

I was planning on doing exactly what you have suggested, parge all insides of external walls then detail tricky areas with PP or the Soudal equivalent.

What is the substrate? Woodcrete / masonry?

[Chanmenie]

3 hours ago, Nickfromwales said:

What is the substrate? Woodcrete / masonry?

 

Isotex woodcrete

[Nickfromwales]

On 25/02/2022 at 11:47, Chanmenie said:

 

Isotex woodcrete

Same as last and current then, as these were / are woodcrete. 
Cementitious parge which was left to dry, then PP applied to all the joints after it had had a couple of weeks to shrink back and dry. Hairline cracks appeared on just about every joint / mortar line, so, parge alone will get you so-so but parge plus PP will get you as good as it gets. 
AT test of 0.88 on current one which was not expected. Tres bien. Only let down by the doors and Windows tbh as I recon the fabric of the build would have scored sub 0.6 if tested independently.

Use SBR on the perimeter of the slab and then seal the walls to the floors also if you want to go for belt ‘n 3 braces. 

(Styrene Butadiene Rubber (SBR), is a water resistant bonding and sealing agent, and shares many similar characteristics with PVA. One key difference is that, whereas PVA remains water soluble after drying, once dry SBR is not. Ed)

Edited February 27, 2022 by MikeSharp01
Added detail for SBR

[Russell griffiths]

@Chanmenie don’t forget all window reveals 

[Chanmenie]

2 hours ago, Russell griffiths said:

@Chanmenie don’t forget all window reveals 

? Yeah I’ll remember, Craig will help with detailing around the windows and doors 

[ruggers]

I agree the wet plaster is a great option for masonry inner leaf, but with 100mm PIR partial fill cavity wall construction I'm looking to add further insulation to the inside of inner leaf whether that be D&D insulated board, or insulated boards on top of wall battens providing space to run some services, or some form of insulation between battens & standard board on top. The latter would have a lot of cold bridging though. A couple of ground floor walls will require water supply pipes dropped down but thats about it. Some rooms I can afford to lose a little off the inside, others not so much but would like to keep insulation thickness consistent. 

 

Looked at blown bead & I don't feel comfortable with certain things I've read plus, I'm in a severe wet/wind driven area with partial face bricks so not recommended after consulting one company.

On 24/02/2022 at 08:54, Nickfromwales said:

Parge needs to be done before joists / wall plates go in / on, and before floor ( deck ) boards go down, to get to all the areas that are often overlooked. This kind of detailing is why one project just got 3.02 ach and another 0.88. 
To achieve air tightness you need to understand all the places which get overlooked and know where to focus your attention. Very easy to get “almost right”, which is basically pointless starting at all. 

Great points there Nick, I never considered parging before the joists go in via hangers or wall plate method same for the trusses and leaving a big enough gap between last truss & gables to be able to parge & add insulation. How are vapour barriers adhered to concrete block walls to prevent an airtight seal with battens over?

On 25/02/2022 at 13:02, Nickfromwales said:

Use SBR on the perimeter of the slab and then seal the walls to the floors also if you want to go for belt ‘n 3 braces. 

Does this mean neat or a lightly diluted SBR painted onto the perimeter of the slab and lapping up onto the walls or in addition to using Purple paint you mentioned. I can't see how SBR alone would form any find of seal?

[JohnMo]

15 minutes ago, ruggers said:

Geat points there Nick, I never considered parging before the joists go in via hangers or wall plate method same for the trusses and leaving a big enough gap between last truss & gables to be able to parge & add insulation. How are vapour barriers adhered to concrete block walls to prevent an airtight seal with battens over?

Does this mean neat or a lightly diluted SBR painted onto the perimeter of the slab and lapping up onto the walls or in addition to using Purple paint you mentioned. I can't see how SBR alone would form any find of seal?

We parged before the wall plate went on. We used hybrid sealant on the the fixing that went through the wall plate, and a good fillet around the plate against the wall.

 

We used blower proof liquid around the whole perimeter at floor/ wall interface.

 

We screwed battens to the wall (ICF Woodcrete) and added hybrid sealant to the screws threads.

 

Do you need vapour barrier on concrete blocks?  We have it on the roof/ceiling, this is bonded to the parge coat at the top of the wall.

 

[Nickfromwales]

1 hour ago, ruggers said:

Does this mean neat or a lightly diluted SBR painted onto the perimeter of the slab and lapping up onto the walls or in addition to using Purple paint you mentioned. I can't see how SBR alone would form any find of seal?

Ah, apologies!

The SBR needs to be applied firstly as dilute, to ‘size’ the substrate, and then applied neat and left to dry before applying tapes or PP. 

So;

Parge, then prime, then seal with tapes or PP. 

[Gus Potter]

Just a thought.. well a couple.

 

SBR is not the same as PVA and they behave in different ways. If you let SBR dry then stuff has less of tendency to stick to it. You can make things worse. SBR is generally meant to be left until it gets tacky then you apply gypsum based or other cementitious materail to it so it forms a chemical bond. Have a look at the SBT technical data sheet before using it to be safe.

 

It's on another thread but the "green plastic" has it's benefits provided you get the rest of the details right and control the quality of the whole job.

 

Up here in Jockland if you turn up to say a domestic loft conversion and ask where are the tapes are they (the Contractor) may suggest you need a deep fried mars bar to rewire your brain. Maybe they do the same in Yorkshire?

 

For all. If you are getting your local builders to price this kind of stuff then be mindful that complex air tighness comes at a cost. If you are new to self build or extending start with the simple stupid, the things you can be comfortable with and able to control quality wise yourself on site. Make it as simple as you can even if seems initially like a comrpomise.

 

Once you get the prices back, if you get many at all, then consider where the weak spots are.. service penetrations, the real howlers.. movement in the structure as it beds in.. can easily be 10 - 15mm and so on if you want good long lasting air tightness. If your aim is just to get a good result at the beginning then why bother going to all the hassle?

 

 

[ruggers]

4 hours ago, JohnMo said:

Do you need vapour barrier on concrete blocks?  We have it on the roof/ceiling, this is bonded to the parge coat at the top of the wall.

 

I don't think a vapour barrier will be required on masonry walls by regs when i receive my completed plans, I'm just considering anything that may help pending the cost of it vs how much it involves. I know the architects plans will mainly just be software pulling over standard data and it will take suggestions to add anything extra to it. I'll be adding a parge coat now, but as others mentioned, these may crack over time especially while bedding in, and once covered with board, it wont be visible. The D&D walls will be getting full perimeter seal, ceilings vapour barrier and I presume internal stud walls too? I thought it might have been a good belt and braces idea to also fix a vapour barrier behind any walls I'm using battens on as I wouldn't have the D&D seal if the parge cracks.

 

The posi joists are an awkward size 253mm high & don't match the block courses, so if allowed, i think a bolted on wall plate attached to the face of the inner leaf would be best to hang joists off then rest on internal walls. If they have to go on the inner leaf, Tony tray or something like the rubber joist seals.

 

What are ceiling vapour barriers adhered to block work with, butyl tape or tube sealant?

Apart from the brick work and slating the roof I'll be involved with most parts either on my own or assisting trades I know or who've been recommended so hopefully can keep it right if I get enough info.

 

Once I start I'll post up any work for others to learn from the good and bad points.

[Nickfromwales]

13 hours ago, Gus Potter said:

SBR is not the same as PVA and they behave in different ways. If you let SBR dry then stuff has less of tendency to stick to it. You can make things worse. SBR is generally meant to be left until it gets tacky then you apply gypsum based or other cementitious materail to it so it forms a chemical bond. Have a look at the SBT technical data sheet before using it to be safe.

PVA is exactly the same. Been using both for decades. The big difference is SBR is far more robust, plus it doesn’t reconstitute with water / damp / moisture etc like PVA does.

Reading the data sheet is deffo good advice, per differing discipline, but if using to size or prime for tapes, you CANNOT apply AT to ‘tacky’ SBR under ANY circumstances. It categorically must be allowed to dry 100%, before applying, or your very expensive tapes will peel straight back off. 
The purpose is to create a surface that is not friable with the dilute applications being applied liberally and allowed to soak in and dry fully.

[BUBBLES67]

On 24/02/2022 at 21:32, Nickfromwales said:

We've had great results with Passive Purple, a spray on or brush applied ( 2 different types ) liquid airtight membrane

Is this something we can do ourselves? Had a quote from intelligent membranes for passive purple which was really expensive. £8k+.  Really wanted t use it for improving air tightness in our new build (brick & block) but costs are already spiralling out of control.

 

[Nickfromwales]

2 hours ago, BUBBLES67 said:

Is this something we can do ourselves? Had a quote from intelligent membranes for passive purple which was really expensive. £8k+.  Really wanted t use it for improving air tightness in our new build (brick & block) but costs are already spiralling out of control.

 

Was that to spray over the entire interior?

[BUBBLES67]

1 hour ago, Nickfromwales said:

Was that to spray over the entire interior?

Yes. except the integral garage.

[OwenF]

On 27/02/2022 at 00:26, ruggers said:

 I thought it might have been a good belt and braces idea to also fix a vapour barrier behind any walls I'm using battens on as I wouldn't have the D&D seal if the parge cracks.

 

@ruggers what did you go for in the end? Did you add insulation internally with membrane & battens for services?

 

I struggled to find any real examples of internal insulation to cavity walls, than also consider stringent airtightness detailing.

[ruggers]

@OwenF Hi, just seen this. I haven't got that far, my project had to be put on hold for the time being. When I completed a full heat loss survey, I was surprised that the addition of internal insulated plasterboard over the whole house made minimal improvement to the total heat loss and it was going to add a lot of money onto the build cost. Every little helps, and I'd have to check again but it was something like 0.4Kw improvement for £2500 extra. I couldn't find anything solid on whether or not a masonry build with cavity insulation was better left without insulated plasterboards for thermal mass reasons, or to add it.

In reference to what you've quoted from my older post of adding a vapour barrier behind the battens then adding insulation between them, I'd need to be sure it wasn't going to cause damp from warm and cold surfaces. I think I'd leave the vapour barrier out, apply battens to a parged wall and as long as it was only one room, blower paint could be applied to the sides of each batten if needed.